1. Field of the Invention
The present invention relates generally to capacitive radio frequency (RF) couplers for utility meters, and more particularly to a capacitive radio frequency parallel plate capacitor coupler structure that exhibits very low RF insertion loss (high coupling) while ensuring high electrical isolation, that meets or exceeds current industry safety standards, between a wireless Network Interface Card (NIC) RF connection and the external antenna of an electricity utility meter enclosed within vandal proof enclosures, typically manufactured from metal or other materials, which cannot be penetrated by radio frequency signals.
2. Background Discussion
In response to climate change nations around the world have recognized the urgent need to reduce carbon emissions and energy consumption. Governments in the United States, Canada, China, and Europe have begun adopting the SMART Grid technology as a means of stimulating depressed economies with green-tech jobs and by passing significant stimulus packages to subsidize utilities that are installing wireless-enabled automated (or advanced) metering infrastructure (AMI) and Smart Utility Meters. [As used herein, “SMART meters” refer to any kind of utility meter that records consumption and transmits recorded data back to a utility company on a predetermined basis.]
Even though Smart meter deployment rates have risen into the tens of millions of units per year, it is nonetheless estimated that 5%-10% of Smart utility meters, with internal antennas, cannot be read remotely due to insufficient local wireless coverage, underground installations, or signal loss caused by installation in vandal proof metal enclosures. Ironically in such cases utilities are forced either to continue reading the Smart meter manually, which undermines the return on investment and carbon emission objectives, or they can install an external remotely located antenna to increase the radio signal strength at the meter site and enable remote network connectivity.
Typically the decision to use a remote external antenna is made by an installer, and in making such a decision, careful consideration must be given to electrical safety of the installation. In low-cost residential meter installations, the power supply to the radio modem (sometimes called a Network Interface Card (“NIC”)) is frequently not isolated from a high AC supply voltage. For an external antenna, this installation scenario dictates the use of a device that can safely isolate the NIC radio frequency (RF) connection to the remote external antenna while enabling a low-loss RF connection with a high degree of RF coupling for the external antenna. The traditional means used for such RF coupling, including, for instance, an external flex antenna placed on the outside of the meter cover to loosely couple to the internal antenna, are ‘make-shift’ in nature, highly inefficient, and result in typical coupling losses of −5 dB to −6 dB. Other proprietary forms of power isolation that have been developed use lumped element components (such as inductors and capacitors) that result in narrow band solutions with inherent reliability issues.
Thus, there remains a need for electric utilities to have a safe and efficient (low loss) means for routing an RF cable from an NIC inside the utility meter to an external remote antenna, so as to boost the wireless signal at certain installation sites.